Projection display systems illuminated by laser light may use a microdisplay, such as a digital micromirror device (DMD), transmissive or reflective liquid crystal display (LCD), liquid crystal on silicon (LCoS), ferroelectric liquid crystal on silicon, deformable micromirrors, and so forth, or a scanning mirror to generate an image on a display plane. In general, a microdisplay in a projection display system will create a miniature version of the image to be displayed and through the use of optical lenses and elements, project an enlarged version of the image on the display plane.
FIG. 1 illustrates a simplified scanning mirror display system 100. The scanning mirror display system 100 may create an image on a display plane 105 by scanning a light spot created by a light source, such as a laser light source 110, over the display plane 105. A scanning mirror 115 may be used to scan the light spot over the display plane 105 and individual picture elements may be created by modulating the light spot. In the scanning mirror display system 100, one or more scanning mirrors may be used to create the image on the display plane 105. If a single scanning mirror is used, then the single scanning mirror may have two degrees of freedom to move the light spot to create a two-dimensional image. If two scanning mirrors are used, then each scanning mirror may have a single degree of freedom to move the light spot to create a one-dimensional beam of light. The combination of the two one-dimensional beams of light created by the two scanning mirrors may create a two-dimensional image. A cathode ray tube television may be analogous to a scanning mirror display system wherein a scanned beam of electrons and a phosphor coated screen replace the scanned light spot and the display plane.
FIG. 2a illustrates a detailed view of a prior art scanning mirror 115. The scanning mirror includes a movable mirror 205 having two degrees of freedom. A first motion unit 210 may move the movable mirror 205 along a first of the two degrees of freedom and a first sensor 211 may detect movement of the movable mirror 205 along the first degree of freedom. A second motion unit 215 may move the movable mirror 205 along a second of the two degrees of freedom and a second sensor 216 may detect movement of the movable mirror along the second degree of freedom. The first motion unit 210 and the second motion unit 215 may make use of electrostatic forces to move the movable mirror 205. Alternatively, the first motion unit 210 and the second motion unit 215 may be micromotors. The first sensor 211 and the second sensor 216 may be used to detect the movement of the movable mirror 205 as well as provide positional information regarding the position of the movable mirror 205.
FIG. 2b illustrates a detailed view of a prior art scanning mirror 115. The scanning mirror 115 includes two movable mirrors, a first movable mirror 255 and a second movable mirror 265. A first motion unit 260 may move the first movable mirror 255 along a first degree of freedom and a first sensor 261 may be used to detect the movement of the first movable mirror 255. A second motion unit 270 may move the second movable mirror 265 along a second degree of freedom and a second sensor 271 may be used to detect the movement of the second movable mirror 265.
In some instances, the scanning mirror 115 may fail, such as when a pivot of the movable mirror 205 becomes jammed or is broken. Additionally, the first motion unit 210 or the second motion unit 215 or both may fail. Due to the high intensity of the light spot produced by the laser light source 110, the scanning mirror display system 100 with the scanning mirror 115 that has failed may pose a health hazard to viewers of the scanning mirror display system 100. FIG. 3 illustrates a hazardous situation arising from a scanning mirror display system 300 with a failed scanning mirror 305. If viewers were to look directly into a light path of the scanning mirror display system 300, it may be possible for viewers to look directly into the light spot. Extended viewing of the light spot may cause damage to eyes 310 of the viewers.
Scanning mirror display systems utilizing scanning mirrors with sensors, such as the scanning mirror 115 shown in detail in FIG. 2, may be able to detect the failure of the scanning mirror 115 through information provided by the first sensor 211 and the second sensor 216. However, it may be possible for the sensors (the first sensor 211 and the second sensor 216) to fail and provide inaccurate information regarding the operation of the movable mirror 205.